1. Field of the Invention
This invention pertains to the field of antennas for electromagnetic radiation. In particular, it is an antenna having coaxial radiating elements with applicability to spacecraft and other devices where a well defined null in the radiation pattern is desired.
2. Description of the Prior Art
A prior art search uncovered the following U.S. patent references:
U.S. Pat. No. 4,041,499 is a tracking feed antenna employing TE.sub.21 mode (FIGS. 3b and 6) and TE.sub.11 mode only. The TE.sub.11 mode produces no null (FIG. 4a) while the TE.sub.21 mode produces only a narrow null (FIG. 4b). While the present invention can be configured to operate in the TE.sub.21 mode, it finds its greatest applicability in the TE.sub.31 and higher order modes, where broader nulls can be realized. Further, the '499 patent does not show flared ends on its radiating elements, as in the present invention. A null is not deliberately formed and shaped as in the present invention. Additionally, the '499 patent uses dielectric 38 within the cavity for other than mechanical reasons, unlike the present invention's strictly mechanical use of dielectric.
U.S. Pat. No. 3,864,687 operates only in the TE.sub.21 mode and does not disclose flares.
U.S. Pat. No. 3,665,481 operates only in the TE.sub.11 and TM.sub.01 modes.
U.S. Pat. No. 3,581,311 operates only in the TE.sub.11 and TEM modes and does not disclose flares.
U.S. Pat. No. 3,508,277 operates only in the H.sub.11 mode.
Secondary references are U.S. Pat. Nos. 3,739,386 and 4,110,751.
The present invention differs from all of the above references in that it is the only device showing operation at TE.sub.31 and higher order difference modes in a coaxial antenna. Further, it is the only device showing operation in the TE.sub.21 and higher order difference modes with a flared radiating element design, thus permitting deliberate null shaping.